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In numismatics, the term milled coinage (also known as machine-struck coinage) is used to describe coins which are produced by some form of machine, rather than by manually hammering coin blanks between two dies (hammered coinage) or casting coins from dies. From Wikipedia

Counterstamped
A countermarked, punchmarked or counterstamped coin is a coin that has had some additional mark or symbol punched into it at some point during its career as a circulating coin. This practise is now obsolete.
Wikipedia